A helicopter is known, which has a rotor or rotors above a fuselage and can perform upward and downward movement, forward and backward flight, hovering and the like. When the number of rotor blades of the helicopter is N (N is a natural number), the rotor(s) generates the N/Rev vibration. In addition, vibration other than the N/Rev vibration is generated based on influence of the wind that the helicopter receives. The helicopter is desired to be superior in interior comfort and to reduce the vibration propagating to crew in the helicopter.
The specification of the US patent application publication No. US2006/0151272A1 and the literature of “Dynamically tailored airframe structures program” disclose techniques of reducing vibration by moving a liquid mass by an actuator using a piezoelectric device.